Slow wave circuit with flexible support



Aug. 3, 1965 J. E. SlDOTl SLOW WAVE CIRCUIT WITH FLEXIBLE SUPPORT Filed July 16. 1962 FIG.4

INVENTOR. JOSEPH E. SIDOTI ATTORNEY I ll 0 {/3 "00 00 0 0 0 5 '0 00 0 0 0 0 0000044 9 9 9 4000 00 0 0 0 0 0 0 0 0 0 0 0 0 0 00000 0 0 0 0 0 0 0 0 0 000000000 0 0 0 0 b00w0w0w0wo United States Patent 3,1935% SD03] WAVE (IHRCUT WITH FLEXEEE Sidcti, Middletown, NJ, assignor to S-F-ll) cries, u, Union, Null, a corporation oi New File July 15, 1962, Ser. No. M93626 6 @laims. (i. sis-ous) (Mug (lizwavelengtu reference operating frequency, and n:(), 1, 2, etc.) between two spaced apart short circuiting planes. Slow-wave circuits employing an array of such elements are characterized by high interaction impedance and higher power handling capabilitie For example, a typical device which operates over the frequency range of 1150 to 1300 megacycles and which produces an output power on the order or 109 kilowatts with a gain of db is less than 19 long and 4 in diameter. Since a great deal of power is handled by this relatively small tube, a large amount or heat is generated in the tube causing it to operate over a wide temperature range as, for example, C. to 200 C. When such a tube heats up many of the parts will expand and change the tube dimensions thereby changing its operation. And during operation of the tube there will be a ditference in expansion of the rods at the input end of the tube from those toward the output end of the tube since the beam current intercepted by the rods gradually increases around the tube from input to output. One of the most critical dimensions in such a tube is the spacing and alignment of the anode circuit for proper wave-electron stream interaction.

According to the present invention, a slow-wave structure is provided wherein an array of conducting elements are distributed along the path of wave propagation sup ported between two spaced apart shorting members. One of the shorting members is constructed so as to be flexible for distortion thereof rather than allowing distortion of the conducting elements when the conducting elements heat up in a tube in operation.

The object of the present invention is to provide a tem erature stable wave propagating structure including an array of conducting elements.

One feature of the present invention is the provision of slow-wave structure comprising an array of conducting elements distributed along the path of wave propagation and supported between first and second spaced apart shorting members, the conducting elements being supported from the shorting members and one of the shorting members constructed in a flexible manner to permit distortion thereof and allow for thermal expansion of the conducting elements.

Another feature of the present invention is the provision of a novel slow-wave structure according to the last aforementioned feature wherein the flexible shorting member is provided with slots therein extending from one edge thereof past the portion thereof supporting the conducting elements whereby the portion of the shorting "ice member supporting the conducting elements can move due to expansion of the conducting elements without causing movement of the entire shorting member.

These and other features and advantages of the present invention will become more apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein:

Flu. 1 is a side cross sectional view of a crossed-field amplifier utilizing features of the present invention,

FIG. 2 is a cross sectional view of a portion of the structure of FIG. 1 taken along line 22 in the direction of the arrows,

FIG. 3 is an isometric view of the flexible anode mounting means shown in FIGS. 1 and 2, and

FIG. 4 is an isometric view of a slow-wave structure with a different flexible mounting means in accordance with the present invention.

Referring now to FIGS. 1-3 i.lustrating a crossed-field amplifier tube utilizing the present invention, the tube comprises an evacuated envelope 11 provided with a cathode electrode assembly 12 axially located therein and an anode electrode assembly 13 surrounding and spaced from the cathode assembly 12 to define a wave-electron ream interaction region 14 therebetween.

The cathode electrode assembly 12 includes a continuous cylindrical cold cathode 15 made of a material having a high secondary emission ratio, such as berylliumcopper, which is supported coaxially within the tube by means of a shaft 16 of, for example, copper extending through the lower of a pair of annular header members 17 which are made of a magnetic material as, for example, iron to serve as pole pieces. The shaft 16 serves as the cathode connection for the tube and is electrically insulated from the remainder of the tube by means of an annular insulator 19 of, for example, glass. The cathode is provided with a pair of end hats 21 of, for example, iron which confine the emitted electrons to the interaction region 14 between the cathode assembly 12 and the anode assembly 13.

The anode assembly 13 includes an array of half-wave resonant conducting rods or elements 22 of, for example, molybdenum which are distributed along spaced apart top and bottom shorting members 23 and 24, respectively, of, for example, copper forming a slow-wave structure. The top shorting member 23 is a thick rigid member provided with a plurality of bores spaced about the circumference thereof to receive a reduced diameter top end portion 25 of the conducting rods 22 which are then fixedly secured to the top shorting member 23 as, for example, by brazing. The bottom shorting member 24 is a flexible member, very thin with relation to the top shorting member 23. For example, while the top shorting member 23 may be on the order of .625", the bottom shorting member 24 for the same assembly would only be .050. The bottom shorting member 24 is provided with apertures therethrough evenly spaced around the circumference thereof to receive the reduced diameter bottom end portion as of the conducting rods 22. The bottom end portion 26 of the rods 22 are then fixedly secured to the bottom shorting member as, for example, by brazin By thi construction a temperature stable circuit is provided. For example, electron tubes utilizing an anode structure constructed in the above manner are operable over the temperature range of 25 to 250 C. without any appreciable elfect on the performance of the tube in' which they are placed. Each rod 22 can independently seek its own length determined by its temperature. In previous slow-wave circuits wherein the conducting rods of the circuit were rigidly supported at both ends the sideways bowing affect on the rods was on the order of 106 times the longitudinal thermal expansion of the rods when the length of the rod was long with respect to the amount of thermal expansion, this usually being the case.

While it is advantageous to have the anode conducting rods 22 supported at one end in a rigid member and at the other end in a flexible member as described above,

both of the shorting members 23 and 24 can be fiexible.

members to allow for thermal expansion of the conducting elements 22. However, such an arrangement is undesirable because of the possibility that the conducting elements 22 can move out of alignment due to oppositely directed movements of the shorting members 23 and 24.

As an alternative embodiment of the present invention a bottom shorting member 24 (see FIG. 4) can be provided wherein slots are cut into the bottom shorting member 24 between conducting rods 22 and past the portion 24" of the bottom member 24' supporting the conducting rods 22 whereby the portions 24" of the bottom shorting member 24 supporting the conducting rods 22 can move due to the expansion of the conducting rods 22 without causing movement of the entire bottom shorting member 24". Thus the unslotted edge of the bottom shorting member 24 can be fixed to a portion of the tube structure while the conducting rods 22 are still permitted to expand longitudinally Without bowing. Since each rod 22 is supported on a portion 24 which is free to move with respect to the next portion 24" thereto, this arrangement shown in FIG. 4 better permits differential thermal expansion of adjacent rods which may be caused by greater electron interception on certain conducting rods 22.

A thin metallic foil of, for example, copper 1 mill thick can be brazed over the slots in the shorting member 24' to avoid the change in anode structure center frequency of a few percent due to the slots cut in the shorting member 24. On the other hand, this change in frequency can be taken into account when originally selecting the dimensions of the anode structure.

The axial standing wave pattern established on such resonant elements exhibits characteristic regions of high electric field intensity, referred to herein as capacitive regions, and characteristic regions of high magnetic field intensity, referred to herein as inductive regions. In the structure of FIGS. 1-4 a capacitive region C exists near the center of the conducting rods 22 and an inductive region L exists near the shorted ends of each rod (see FIG. 1).

In order to increase the interaction bandwidth of the slow-wave structure and insure forward wave interaction each conducting rod 22 is provided in the central capacitive region thereof with a conducting member 27 of, for example, copper with extending portions 23 of, for example, copper disposed in spaced apart relationship with respect to the extending portions 28 of conducting members 27 on the two alternate conducting rods 22 closest thereto to form capacitive coupling gaps 29 therebetween. One band of conducting members 27 couples one set of alternate conducting rods 22, and a second hand couples the remaining rods 22.

The slow-wave structure is interrupted to provide a drift segment 30. On opposite sides of the drift segment 30 input and output coaxial lines 31 and 32, respectively, are mounted on shorting members 23 and 24 with the axes of coaxial lines 31 and 32 parallel to the axes of the conducting rods 22 of the anode assembly 13. The coaxial lines 31 and 32 project out of opposite ends of the envelope 11 and have their axes parallel with the tube axis.

Each of the coaxial lines 31 and 32 has an outer conductor 33 of, for example, copper and a center conductor 34 of, for example, copper and is provided with a vacuum tight Wave permeable window (not shown) of, for example, alumina ceramic sealed between the outer and center conductors 33 and 34, respectively A conducting pin 3i; of, for example, copper connects the next adjacent conducting rods 22 to the center conductors 34 of input and output coaxial lines 31 and 32 to couple the coaxial lines 31 and 32 to the remainder of the slowwave circuit.

The tube is evacuated and sealed by means of a pinch off tube 37.

A vertically directed magnetic field is provided in the interaction region 14- by means of a solenoid 38 coaxially aligned with and surrounding the tube. The crossed electric field in the region 14 is provided by means of a negative voltage supply 13 applied via leads between the grounded anode and the cathode shaft 16.

In operation, a signal which it is desired to amplify is fed to the slow-wave circuit of the anode electrode assembly 13 via the input coaxial line 31. This signal establishes a traveling-Wave in the interaction region 14 of sullicient intensity to initiate the emission of electrons from the cold cathode l5, and this emission can be sustained by secondary emission due to back bombarding electrons which have gained energy from the wave without the necessity of supplying external heating power.

The interacting electron stream moves through the region 14 with a clockwise circumferential velocity determined by the ratio of electric-to-magnetic field. The phase velocity of the travelingavave is approximately synchronous with this electron stream velocity for a wide band of frequency so that the electrons deliver energy to and amplify waves within this band, the amplified output signal being taken out through the output coaxial line 32. The drift segment 36 is of sufficient length to permit electron debunching so that electrons may re-enter the interaction region for improved efficiency without producing undesired internal feedback.

While the invention has been described with respect to circular crossed-field amplifiers it is adaptable for the circuit of a magnetron oscillator. Also, it is useful in planar type tubes which utilize a circuit or" the type desired. For example, the invention can be used in socalled M-type tubes and O-type tubes to support a linear array of conducting elements. However, the linear shorting member in such tubes will not be as desirable as the circular shorting member in a cylindrical tube since the circular shorting member is less subject to distortion in its own plane than a linear member.

Since many changes could be made in the above construction and many apparently Widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A slow-wave structure comprising (a) an array of conducting elements distributed along the path of wave propagation, and

(b) first and second spaced apart shorting members shorting the ends of said conducting elements,

(1) one end of said conducting elements rigidly supported on said first shorting member, (2) the other end of said conducting elements supported on said second shorting member, and (3) said second shorting member being a flexible member, thin with respect to the thickness of said first shorting member, and adapted to allow distortion thereof due to thermal expansion of said conducting elements. 2. The slow-wave structure of claim 1 wherein said second shorting 'member is provided with slots therein extending from one edge thereof past the portion thereof supporting said conducting elements whereby portions of said second shorting member supporting said conduct ing elements can move due to expansion of said conducting elements without causing movement of the entire second shorting member.

3. An electron discharge device comprising, in combination,

(a) first extended electron emitting electrode means,

(b) second extended electrode means being spaced from said first electrode means for forming an interaction region therebetween,

(c) an array of axially aligned conducting elements connected to said second electrode means and distributed along the length thereof,

(d) first and second spaced apart shorting means conmeeting the ends of said conducting elements, said second shorting means being a flexible member, thin with respect to said first shorting means,

(e) coupling means for extracting microwave energy from said array,

(f) means for generating a voltage between said first and second electrode means which establishes a unidirectional electric field in said interaction region, and

g) means for establishing a unidirectional magnetic field in crossed relation with respect to said electric field whereby electrons emitted from said first electrode into said interaction region deliver energy to a slow-wave on said second electrode means.

4. The electron discharge device of claim 3 wherein (a) said first electrode means is cylindrically shaped,

(b) said second electrode means is coaxially spaced from said first electrode means to form a hollow cylindrical interaction region, and

(c) said first and said second shorting means are cylindrically shaped with said conducting members fixedly secured thereto.

5. The electron discharge device of claim 4 wherein said second shorting member is provided with slots therein extending from one edge thereof past the portion thereof supporting said conducting elements whereby portions of said second shorting member supporting said' conducting elements can move due to expansion of said conduction elements without causing movement of the entire second shorting member.

6. A slow-wave structure assembly for an electron discharge tube comprising (a) an array of elongated resonant conducting elements distributed along a desired path of wave propagation and (b) means for supporting a plurality of said elongated elements at a pair of axially spaced positions on said elements, one of said supporting means being flexible relative to the other for supporting said conducting elements whereby during heating of the slow-wave structure the flexible mounting means will allow the conducting elements to freely expand axially without distortion.

References Cited by the Examiner UNITED STATES PATENTS 2,242,275 5/41 Varian 3l3297 2,505,529 4/50 Crawford et a1. 31539.55 2,564,385 8/51 Warnecke et a1. 3l55.48

GEORGE N. WESTBY, Primary Examiner. 

3. AN ELECTRON DISCHARGE DEVICE COMPRISING, IN COMBINATION, (A) FIRST EXTENDED ELECTRON EMITTING ELECTRODE MEANS, (B) SECOND EXTENDED ELECTRODE MEANS BEING SPACED FROM SAID FIRST ELECTRODE MEANS FOR FORMING AN INTERACTION REGION THEREBETWEEN, (C) AN ARRAY OF AXIALLY ALIGNED CONDUCTING ELEMENTS CONNECTED TO SAID SECOND ELECTRODE MEANS AND DISTRIBUTED ALONG THE LENGTH THEREOF, (D) FIRST AND SECOND SPACED APART SHORTING MEANS CONNECTING THE ENDS OF SAID CONDUCTING ELEMENTS, SAID SECOND SHORTING MEANS BEING A FLEXIBLE MEMBER, THIN WITH RESPECT TO SAID FIRST SHORTING MEANS, 